The size of portable wireless communications devices, such as telephones, continues to shrink, even as more functionality is added. As a result, the designers must increase the performance of components or device subsystems while reducing their size, or placing these components in less desirable locations. One such critical component is the wireless communications antenna. This antenna may be connected to a telephone transceiver, for example, or a global positioning system (GPS) receiver.
Wireless communications devices, a wireless telephone or laptop computer with a wireless transponder for example, are known to use simple cylindrical coil antennas as either the primary or secondary communication antennas. The resonance frequency of the antenna is responsive to its electrical length, which forms a portion of the operating frequency wavelength. The electrical length of a wireless device helical antenna is often an odd multiple of a quarter-wavelength, such as 3.lambda./4, 5.lambda./4, or .lambda./4, where .lambda. is the wavelength of the operating frequency, and the effective wavelength is responsive to the dielectric constant of the proximate dielectric.
Wireless telephones can operate in a number of different frequency bands. In the US, the cellular band (AMPS), at around 850 megahertz (MHz), and the PCS (Personal Communication System) band, at around 1900 MHz, are used. Other frequency bands include the PCN (Personal Communication Network) at approximately 1800 MHz, the GSM system (Groupe Speciale Mobile) at approximately 900 MHz, and the JDC (Japanese Digital Cellular) at approximately 800 and 1500 MHz. Other bands of interest are global positioning satellite (GPS) signals at approximately 1575 MHz and Bluetooth at approximately 2400 MHz.
Typically, better communication results are achieved using a whip antenna, as opposed to the above-mentioned helical antennas. Using a wireless telephone as an example, it is typical to use a combination of a helical and a whip antenna. In the standby mode with the whip antenna withdrawn, the wireless device uses the stubby, lower gain helical coil to maintain control channel communications. When a traffic channel is initiated (the phone rings), the user has the option of extending the higher gain whip antenna. Some devices combine the helical and whip antennas. Other devices disconnect the helical antenna when the whip antenna is extended.
The whip antenna has a physical length, when extended, related to the antenna operating frequency. When withdrawn, the whip antenna must fit within the constraints of the wireless device chassis. Therefore, as the wireless device chassis decreases in size, the extended length of conventional whip antennas has necessarily decreased. A shorter whip antenna can be made to operate at the same frequency as longer whip antennas by using higher dielectric constant materials in the antenna fabrication. However, the use of higher dielectric constants makes for a lower gain antenna, and a poorer performing wireless device.
One popular solution to the above-mentioned length problem has been to fabricate the whip antenna as a wire with a telescoping tube section. When the antenna is withdrawn, the wire section is withdrawn into the tube, with the tube being withdrawn into the chassis. When extended, the combination of the wire and tube section defines the antenna length.
Many wireless telephones that are noted for their small size still have a whip antenna portion extending from the chassis body, even in the withdrawn position. This extending portion can become tangled in a trouser pocket or purse as the user extracts the phone to answer a call. One solution to this problem is to wear a belt-mounted holster to carry the phone, or to mount a belt clip on the phone. However, this solution at least partially defeats the purpose of making the phone small enough to be pocketsize.
It is known to use a portion of a circuit board, such as a dc power bus, as an electromagnetic radiator. This solution eliminates the problem of an antenna extending from the chassis body. However, these radiators are extremely inefficient “antennas”, typically providing poor gain and directionality. These types of radiators are also susceptible to crosstalk from other signals on the board. Further, these types of radiators can also propagate signals that interfere with digital or radio frequency (RF) on the circuit board. Electromagnetic communications through these radiators can also be shielded by other circuits, circuit groundplanes, the chassis, or other circuit boards in the chassis.
It would be advantageous if an efficient antenna could be developed that did not extend out from the chassis body of a wireless phone, as a typical whip antenna does in the withdrawn position.
It would be advantageous if a wireless telephone chassis could be made with minimal extending portions, such as the extending portions resulting from the housing of antennas.
It would be advantageous if an efficient antenna could be formed on a wireless telephone circuit board.